A UNIX program should use its name as the first word in error messages
it prints.
That's important when the program is running in the background or as part
of a pipeline - you need to know which program has the problem:

someprog: quitting: can't read file xxxxxx

It's tempting to use just the program name in the echo commands:

echo "someprog: quitting: can't read file $file" 1>&2

but if you ever change the program name, it's easy to forget to fix the
messages.
A better way is to store the program name in a shell variable at the top of
the script file, and then use the variable in all messages:

Even better, use the $0 parameter.
The shell automatically puts the script's name there.
But $0 can have the absolute pathname of the script, such as
/xxx/yyy/bin/someprog.
The
basename (45.18)
program fixes this: basename strips off the head of
a pathname - everything but the filename.

For example, if $0 is /u/ehuser/bin/sendit, then:

myname="`basename $0`"

would put sendit into the myname shell variable.

Just as you can make
links (18.3)
to give UNIX files several names,
you can use links to
give your program several names (45.13).
For instance, see the script named ll, lf, lg (...and so on)
in article
16.7.
Use $0 to get the current name of the program.